1. Field of the Invention
The present invention relates to a packing material for liquid chromatography, comprising particles having a silicone polymer film coated on substantially the entire surface thereof.
2. Description of the Related Art
Recently, there have been increased developments in analysis or purification techniques using high performance liquid chromatography. In some cases, purification is carried out on a commercial scale using an extra large liquid chromatograph column. In such analysis or purification, the qualities of a packing material in a column are very important.
It is believed that about 80 percent of high performance liquid chromatography for analysis or purification is currently carried out by means of reversed phase liquid chromatography. Various methods have been disclosed using an ODS (octadecylchlorosilane)silica gel (i.e., C.sub.18 -type) packing material which is prepared by chemically bonding dimethyloctadecylchlorosilane to silanol (Si--OH) groups of silica gel. Other packing materials or supports for reversed phase liquid chromatography are known, for example, a C.sub.8 -type packing material prepared by bonding dimethyloctachlorosilane to the silanol groups of silica gel; a C.sub.4 -type packing material prepared by bonding dimethylbutylchlorosilane; a C.sub.1 -type packing material prepared by bonding trimethylchlorosilane, and a phenyl-type packing material prepared by bonding triphenylchlorosilane, and the like.
In the bonded type packing materials or supports conventionally used for reversed phase liquid chromatography, however, 10-20% of the silanol groups remain unreacted because of an incomplete reaction between the silanol groups and alkyl or phenylchlorosilane. It is generally considered that the larger becomes the molecular weight of the silane compound, the more unreacted silanol groups remain; namely, EQU C.sub.18 -type&gt;C.sub.8 -type&gt;C.sub.4 -type&gt;C.sub.1 -type.
The presence of such residual silanol groups is a serious problem in reversed phase liquid chromatography. In the analysis or purification of a polar substance, the residual silanol groups, if any, strongly interact with the polar substance. Thus, such an analysis or purification results in a wide peak and tailing. Further, a highly polar substance irreversibly adsorbs such residual silanol groups. Thus, the function of a column packed with such a conventional material is rapidly deteriorated. In addition, the presence of a hydrophilic surface of the silica gel as well as residual silanol groups thereon causes a conventional packed column to become weak against acids and alkalis, and thus limits the pH region of a mobile phase solvent to within 2 to 7.
In order to solve the problems mentioned above, and the like, some conventional packing materials prepared by a reaction with dimethyloctadecylchlorosilane or dimethyloctylchlorosilane have been treated again with trimethylchlorosilane (TMS) or the like, so as to block the residual silanol groups. But, such a post-treatment with TMS cannot completely avoid the presence of residual silanol groups, and a high quality packing material without such residual silanol groups has not been developed for reversed phase liquid chromatography. In addition to the above incomplete blocking of the residual silanol groups by the post-treatment with TMS, the problem of a low resistance to acids and alkalis, due to the presence of an exposed hydrophilic surface of the silica gel has arisen.